The application generally relates to an economized refrigeration system. The application more specifically relates to an economized refrigeration system having an auxiliary compressor dedicated to economizer flow.
In refrigeration systems, a refrigerant gas is compressed by a compressor and passed to a condenser where it exchanges heat with another fluid such as the ambient air. From the condenser, the pressurized liquid refrigerant passes through an expansion device and then to an evaporator, where it exchanges heat with another fluid that is used to cool an environment. The refrigerant returns to the compressor from the evaporator and the cycle is repeated.
Economizer circuits are utilized in refrigeration systems to provide increased cooling capacity for a given evaporator size, and also to increase efficiency and performance of the system. An economizer circuit utilizing one or more additional expansion devices is sometimes incorporated just downstream of the condenser. For a system utilizing one additional expansion device, the primary expansion device expands the refrigerant from condenser pressure to an intermediate pressure, resulting in flashing of some of the refrigerant to its vapor state. The flashed refrigerant is reintroduced into the compression stage and provides some cooling during compression as the saturated vapor is mixed with the superheated vapor refrigerant. Cooling during compression results in some reduction to compressor input power. The remaining liquid refrigerant at the intermediate pressure from the primary expansion device is at a lower enthalpy. The additional expansion device expands the lower enthalpy liquid refrigerant from the intermediate pressure to evaporator pressure. The refrigerant enters the evaporator with lower enthalpy, thereby increasing the cooling effect in refrigerant systems with economized circuits versus non-economized systems in which the refrigerant is expanded directly from the condenser.
One traditional method of enabling an economized refrigeration system is through the use of a flash tank and an additional expansion device. In flash tank economizer circuits, the primary expansion device is provided upstream of the flash tank. Liquid refrigerant flows through the primary expansion device and into the flash tank. Upon passing through the primary expansion device, the liquid refrigerant experiences a substantial pressure drop, whereupon, at least a portion of the refrigerant rapidly expands or “flashes” and is converted from a liquid phase to a vapor phase at an intermediate pressure. The remaining liquid refrigerant gathers at the bottom of the tank for return to the main refrigerant line upstream of the additional expansion device. Vapor refrigerant is returned to the compressor, either at the compressor suction or to an intermediate stage of compression. As a result of the intermediate pressure of refrigerant gas in the flash tank, the gas returned to the compressor requires less compression, thereby increasing overall system efficiency.
Introducing the gas refrigerant from a flash tank economizer to one of the intermediate pressure compressor suctions or other stage in multi-stage compressors can be problematic. Typically, the first stage compressor handles the flow from the evaporator while a higher stage compressor handles the flow from the first stage compressor discharge as well as the flow from the economizer. In this arrangement, the economizer operating conditions are dictated by the overall system conditions and operating point; no method is available to independently control the economizer operating pressure and flow rate. Without such independent control, the economizer and second stage compressor must be designed for specific operating conditions. Off-design operating conditions result in a compromise in economizer performance, and consequently in overall system performance. In addition, this system requires multiple compression stages in series between the evaporator and condenser to incorporate the economizer.
Even more difficult is introducing the gaseous refrigerant from the economizer in systems having only single-stage compressors because there is no mechanical means to operate the compressor at a pressure level between the evaporator and condenser. Thus, the economizer operating conditions are dictated by the overall system conditions and operating point.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.